In the art of commercial airplane design, there are possible situations when some of the aircraft doors cannot be used in a ditching (i.e. water landing) situation because immediately after landing on water, the water line is higher than the airplane door threshold (i.e. the door sill is negative).
Even in cases when the door sill is positive, but the water line is just a few inches lower than the door threshold, a particular door can be considered as not being usable for passenger egress subsequent to ditching. These situations may occur on multi-deck commercial airplanes, high-wing airplanes, mid-wing airplanes, and short narrow body low-wing airplanes. The door may be considered as not being usable for passenger egress for several reasons. One of the reasons is that the airplane will sink faster than it is getting lighter due to the passenger egress, so the door sill becomes negative faster than the certification requirements for a positive door sill state. Even if the door sill does not decrease, the marginally positive sill allows for waves and splashes to enter into the cabin, thereby increasing the airplane sinking rate.
As such, there is a need for a design that will allow for an evacuation of an aircraft following a water landing with a marginally positive door sill.